As there are different chips implementing the ADC functionality on the different modules, there are slightly different attributes which need to be considered for compatibility amongst the full range of Apalis/Colibri modules:

One sample measurement on one channel takes about 450-550us for codec types UCB1400 and WM9715.
The analog inputs are implemented with the resistive touch H/W. Touch events can lead to increased ADC channel sampling intervals.

If you need a faster(high sampling rate) or more precise ADC(higher resolution) or ADC with more channels, you can add another external ADC chip.
The Colibri module has different interfaces(I2C, SPI, etc.) to connect an ADC, a very common one is the SPI interface.